How the worst screw-up in Oscars history happened

• Academy accounting firm PriceWaterhouseCoopers released a statement early Monday about the best picture mishap.• "La La Land" was accidentally awarded best picture when it was "Moonlight" which actually won.• According to PWC, the presenters were mistakingly "given the wrong category envelope."• 2 cards are created for each winner.

PriceWaterhouseCoopers, the accounting firm in charge of vote counting for the Oscars, released a statement "sincerely apologising" for Sunday night's spectacular best picture blunder.

A statement released by PriceWaterhouseCoopers says the presenters were mistakenly handed the wrong category envelope, resulting in Emma Stone's name being read out as the winner.

The firm has overseen the Academy Awards' vote counting for 83 years. Two cards are created for each winner and handed to a pair of PwC employees who wait in the wings and hand them to the awards presenters.

In a statement, PriceWaterhouseCoopers said:

"We sincerely apologize to Moonlight, La La Land, Warren Beatty, Faye Dunaway, and Oscar viewers for the error that was made during the award announcement for Best Picture.

"The presenters had mistakenly been given the wrong category envelope and when discovered, was immediately corrected. We are currently investigating how this could have happened, and deeply regret that this occurred.

We appreciate the grace with which the nominees, the Academy, ABC, and Jimmy Kimmel handled the situation."

It wasn't until after the cast and crew of "La La Land" were midway through their speeches that the error was realised and producer Jordan Horowitz handed the award to "Moonlight."